Habitat scale and seasonality influence macroinvertebrate functional feeding groups in a tropical Kenyan montane stream

Abstract

Habitat quality and diversity strongly influence the composition of macroinvertebrate communities in lotic ecosystems. We evaluated the  functional organization of macroinvertebrates in response to changes in habitat type and seasonality in the Afromontane Moiben River in  western Kenya. In-stream substrate characteristics were evaluated at the reach, channel unit/habitat and microhabitat scales at nine  sites in different land-use areas. Water and habitat quality were assessed during the dry (January–March) and wet (April–June) seasons. A  total of 81 macroinvertebrate samples were collected every month from three channel units (pools, riffles and runs) defined by different  substrate types and classified into five functional feeding groups (FFGs): collector-filterers, collectorgatherers, predators, scrapers and  shredders. Numerical abundance differed significantly between FFGs, with gatherers > filterers > predators > scrapers > shredders.  Coarse substrate (bedrock, boulders and cobbles) in riffles had the highest richness and abundance of filterers and scrapers while sand,  mud and detritus in pools recorded the lowest richness and abundance. Shredders and scrapers occurred predominantly in upstream  sites with minimal human disturbance, while gatherers were most abundant at disturbed sites. The greatest variability in FFGs was at the  smallest microhabitat scale, and not at the reach scale. This study shows that attention should be given to both reach-scale and in-stream  disturbances when assessing the ecological condition of streams and rivers.